Analog-to-digital conversion (ADC) is to convert a continuously varying analog quantity into a discrete digital quantity. For example, the analog quantity may be an analog signal, and the digital quantity may be a digital signal. According to the conversion manner, a successive approximation analog-to-digital converter, an integration analog-to-digital converter and a voltage-frequency conversion analog-to-digital converter may be used to perform analog-to-digital conversion. The successive approximation analog-to-digital converter (SAR ADC) has a medium conversion precision and a medium conversion speed. Practiced by the CMOS process, the SAR ADC ensures smaller chip area and lower power consumption, additionally implements multi-path conversions and thus has comprehensive advantages in the aspects of precision, speed, power consumption and cost. Therefore, the SAR ADC is extensively applied in industrial control, medical instruments, touch technology and the like fields.
The SAR ADC works under the following basic principles: comparing an analog input signal to be converted with an estimation signal, and determining whether to increase or decrease the estimation signal according to a comparison result, for approximation to the analog input signal. The estimation signal is obtained by an output of a digital/analog (D/A) converter. When the analog input signal is equal to the estimation signal, a digital signal input to the D/A converter is correspondingly a digital quantity of the analog signal.
A dynamic range of the ADC is a specific range in which the ADC is capable of correctly converting an input analog signal into a digital signal when the input analog signal is within this range.
In the prior art, the dynamic range of the SAR ADC is determined by a reference voltage thereof. For example, in a full differential SAR ADC, a positive reference voltage is Vrefp and a negative reference voltage is Vrefn, and then the dynamic range of the ADC is (Vrefp-Vrefn). To ensure that the input analog signal may be correctly converted, generally the range of the SAR ADC needs to be expanded, that is, the reference voltage needs to be increased. As a result, more power is inevitably consumed.
Therefore, how to expand a dynamic range of the ADC changing the value of the reference voltage is a technical problem to be urgently solved in the prior art.